Polyester-based shock-resistant compositions and process for their preparation

ABSTRACT

Polyester-based shock-resistant compositions, endowed with a high shock resistance, particularly at low temperatures comprising: 
     (a) a matrix constituted by one or more unsaturated polyesters; 
     (b) an elastomer constituted by butadiene or acrylic rubbers; and 
     (c) a block-copolyester.

This is a division of co-pending application Ser. No. 07/815,915 filedJan. 2, 1992, now U.S. Pat. No. 5,252,665, which is a continuation ofSer. No. 07/955,098 filed May 28, 1987, now abandoned.

FIELD OF THE INVENTION

The present invention relates to shock-resistant compositions based onpolyesters, and to a process for their preparation.

More particularly, the present invention relates to polyester-basedpolymeric compositions endowed with a high shock resistance,particularly at low temperatures.

BACKGROUND OF THE INVENTION

In U.S. Pat. No. 3,919,353 compositions based on saturated polyestershave been disclosed and claimed, the shock resistance of which wasenhanced by dispersing into them an elastomeric phase constituted bybutadiene rubbers, such as, e.g., polybutadiene or butadiene/styrenecopolymers, or by polyolefinic rubbers, such as, e.g., saturated orunsaturated ethylene/propylene copolymers, which have been previouslycross-linked and modified by a grafting reaction with polar monomers. Inthe grafted and cross-linked elastomer, the cross-linked phase ispresent in an amount of at least 30%, and, preferably, at least 50%.

The shock resistance of such compositions, at room temperature, isconsiderably improved as compared to that of polyesters without such anelastomeric phase; however, their low-temperature shock resistance, inparticular within the range of from 0° C. to -40° C., is not completelysatisfactory for some applications.

New shock-resistant, polyester-based compositions have been nowdiscovered, in accordance with the present invention, which maintainhigh characteristics of shock resistance also at low temperatures.

DETAILED DESCRIPTION OF THE INVENTION

The compositions of the present invention are characterized in that theycomprise:

(a) from 55 to 98% by weight of one or more saturated polyesters;

(b) from 1 to 35% by weight of butadiene and/or acrylic rubber; and

(c) from 1 to 10% by weight of an elastomeric copolyester.

The compositions of the present invention may be obtained by dispersingand/or blending the above-mentioned (a), (b) and (c) components in themolten state, or as solutions in suitable solvents which aresubsequently removed by per se conventional techniques.

The preferred process consists in operating at such temperatures as tohave the (a) and (c) components in the molten state, blending them witheach other, and then dispersing into them the (b) component in the formof small-size particles, preferably with an average diameter within therange of from 0.1 to 2 microns, by using well-known equipment forpreparation of polymeric blends, such as mixers, extruders, and soforth.

During the preparation of these compositions, several additives, such asstabilizers, antioxidants, pigments, dyes, flame-proofing agents,lubricants, organic and inorganic reinforcing agents (carbon fibers orfiberglass, aramidic fibers, talc, asbestos, etc.), nucleating agents,and so on, may be added.

The saturated polyesters (a) used in the compositions of the presentinvention are thermoplastic resins having an intrinsic viscosity of atleast 0.4 dl/g (as measured on a 1:1 phenol/tetrachloroethane mixture),obtained from an aromatic or cycloaliphatic dicarboxylic acid, with adiol having the formula:

    HO--R--OH                                                  (I)

wherein R is a linear or branched alkylene radical containing from 2 to20 carbon atoms, or an arylene or cycloalkylene radical containing from6 to 20 carbon atoms.

Examples of preferred dicarboxylic acids are terephthalic acid,isophthalic acid and cyclohexane-1,4-dicarboxylic acid; examples ofpreferred diols are ethanediol, propanediol, butanediol, and hexanediol.

Some examples of preferred saturated polyesters arepoly(ethyleneterephthalate), poly(propyleneterephthalate), poly(butyleneterephthalate), andpoly(hexamethylene-cyclo-hexane-1,4-dicarboxylate), and their blends.

These polyesters may be produced according to per se known techniquesfor polycondensation or polytransesterification.

The saturated polyesters used in the preparation of the compositions ofthe present invention may possibly contain, however in amounts smallerthan 15% by mol in respect of the aromatic or cyclo-aliphatic acids,aliphatic dicarboxylic acids of from 4 to 20 carbon atoms. As examplesof aliphatic dicarboxylic acids which may be used, adipic acid andsebacic acid may be mentioned.

The (b) component used in the compositions of the present invention maybe a butadiene rubber, or an acrylic rubber.

By the term "butadiene rubber", any elastomeric polymer is meant whichis obtained either by direct polymerization, or by polymerization and asubsequent grafting reaction of butadiene and/or isoprene withethylenically unsaturated monomers, such as, e.g., styrene,acrylontrile, methacrylonitrile, acrylic and methacrylic esters, acrylicand methacrylic acid, maleic acid and anhydride, maleic and fumaricesters, alkylstyrenes, in any combinations with one another. Typicalexamples of butadiene rubbers are the butadiene/styrene/acrylontrile orbutadiene/styrene/methylmethacrylate terpolymers, as well as the sameterpolymers, or polybutadiene, or natural rubber, or butadiene/styreneor butadiene/acrylontrile copolymers subsequently modified by a graftingreaction with a polar monomer, such as acrylonitrile, styrene, acrylicor methacrylic esters, methacrylic acid, maleic acid and anhydride, andso forth.

By the term "acrylic rubbers", any elastomeric polymer is meant which isobtained, either by direct polymerization or by polymerization andsubsequent grafting reaction of alkyl-esters of acrylic or methacrylicacid, containing from 1 to 10 carbon atoms in their alkyl chain, suchas, e.g., ethyl acrylate, butyl acrylate, methyl methacrylate andcyclohexyl methacrylate. Together with these monomers, for the synthesisof the above-said acrylic rubbers, other ethylenically unsaturatedmonomers may also be used, such as, e.g., styrene, alkylstyrenes,acrylonitrile, methacrylonitrile, and/or, in an amount of from 0.1 to 5%by weight, such di- or poly-functional monomers (cross-linking agents)as ethyleneglycol acrylate or methacrylate, glycidyl methacrylate, allylmethacrylate, diallylmaleate, diallylphthalate, hydroxyethylmethacrylate, etc. Typical examples of acrylic rubbers are the polymersobtained from alkylesters of acrylic or methacrylic acid, such as butylacrylate, ethyl acrylate and methyl methacrylate, possibly containingminor amounts, e.g., from 10 to 30% by weight, of styrene oracrylontrile, and small amounts, e.g., from 0.5 to 3% by weight, ofethyleneglycol methacrylate or allyl methacrylate.

Said (b) rubbers are characterized by a main glass transitiontemperature (T_(g)) lower than 0° C., and by a cross-linking degree (gelcontent) within the range of from 0 to 99% by weight, and preferablyfrom 50 to 99% by weight.

The cross-linking may be already present in the rubber before this isblended with the other components, or it may be achieved during saidblending, with the possible further addition of monomers of theabove-indicated types and in the presence of free-radical initiators, orwith the addition of suitable other cross-linking agents, such as, e.g.,diisocyanates, diamines, diols, and so on.

The (c) component used in the compositions of the present invention is ablock-copolyester having a melting point lower than 190° C., obtained bymeans of the polycondensation or transesterification of an aropmaticdicarboxylic acid with a diol having the above formula (I), and with apolyetherglycol having the formula:

    HO--(R.sub.1 --O).sub.m --H                                (II)

wherein R₁ is a linear or branched alkylene radical containing from 2 to20 carbon atoms, and m is an integer higher than 2, and such that themolecular weight of the polyetherglycol is within the range of from 300to 10,000, and preferably from 600 to 4,000.

Examples of suitable polyetherglycols are polyoxytetramethyleneglycol,polyoxyethyleneglycol, polyoxypropyleneglycol, etc., or mixturesthereof.

Said block-copolyesters have a content of rigid segments--by which termis meant segments which are derived from the esterification of the acidwith the diol having formula (I)--within the range of from 10 to 75% byweight. Furthermore, the ratio of the number of carbon atoms to thenumber of oxygen atoms present in the polyetherglycol (II) preferably isequal to, or higher than, 2.

The lower the content of rigid segments in the compositions of thepresent invention, the greater is the improvement of the resiliencethereof caused by the presence of copolyesters (c). More particularly, acontent of rigid segments in the copolyesters, within the range of from30 to 50% by weight, allows a favorable compromise to be made betweenstiffness and shock-resistance and shape stability on heating.

To the compositions of the present invention other thermoplasticmaterials may be added, such as, e.g., any per se known type ofpolycarbonate, in particular that obtained from bisphenol A andphosgene; any known type of thermoplastic polyurethane, and inparticular that obtained from methylene-bis(phenylisocyanate), andpolyether-glycols and/or polyester-glycols. Furthermore, poly(vinylchloride), polyamides, polystyrenes, ABS resins, etc., may be added.

The amount of said thermoplastic materials may vary over a wide range.In particular, amounts of thermoplastic materials lower than 25%, andpreferably within the range of from 1 to 10% by weight, relative to thetotal composition, are recommended.

The compositions of the present invention are mainly characterized by agood low-temperature shock-resistance; more particularly, attemperatures of from 0° C. to -40° C.; they are furthermore endowed withvery good resistance to gasolines, to oils, to light, and tothermo-oxidation. Thanks to these peculiar characteristics, thecompositions of the present invention are particularly suitable for usein certain fields, such as, e.g., in car and motorcycle field (bumpers,fenders, spoilers, side-body moldings, protective helmets, etc.), and inthe sports field (ski-boots, soles for ice skates, etc.), wherein theabove-mentioned characteristics have a considerable importance.

EXAMPLES

For the purpose of illustrating the present invention still moreextensively and in still greater detail, some examples are now supplied,which are in no way to be regarded as being limitative thereof.

EXAMPLES 1-4

By means of a twin-screen extruder MARIS TM 33, at a temperature of 260°C., and with a screw revolution speed of 150 rpm, blends are preparedwhich are constituted by:

(a) polybutyleneterephthalate having a viscosity of 1.4 dl/g;

(b) grafted butadiene/styrene/methylmethacrylate terpolymer with across-linking degree (gel content) of 94% by weight, and a glasstransition temperature (T_(g))=-80° C., manufactured by Rohm and Haasunder the tradename KM 653; and containing from 58-62% by weightpolybutadiene, from 12-18% by weight styrene and from 24-26% by weightmethylmethacrylate--after "KM 653".

(c) copolyesters obtained from terephthalic acid, 1,4-butanediol andpolyoxytetramethyleneglycol, with a molecular weight of about 1000, andhaving different contents of rigid segments, as reported in Table 1below.

During the preparation of said blends, antioxidants, i.e., 0.4% ofIRGANOX 1010 and 04% of IRGAFOS 168, are also added.

The weight ratios of the blend components are reported in Table 1.

Rods from the extruder are pelletized and dried from 2 to 4 hours at80°-140° C. The material is subsequently injection-molded at 260° C. toobtain suitable specimens for property determinations, according to ASTMStandards.

Such properties are reported below in Table 1:

                                      TABLE 1                                     __________________________________________________________________________                            Example No.                                           Composition             1    2    3    4                                      __________________________________________________________________________    (a) Polybutyleneterephthalate                                                                         74.2 74.2 74.2 74.2                                   (b) Rubber KM 653       25   20   20   20                                     (c) Copolyester containing:                                                   33% of rigid segments        5                                                46% of rigid segments             5                                           66% of rigid segments                  5                                      (d) Antioxidants        0.8  0.8  0.8  0.8                                    __________________________________________________________________________                            Example No.                                           Properties     Method                                                                             Unit                                                                              1    2    3    4                                      __________________________________________________________________________    Specific       D.720                                                                              g/cm.sup.3                                                                        1.21 1.21 1.25 1.25                                   Gravity at 23° C.                                                      Yield Strength D.638                                                                              MPa 35   36   35   35                                     VICAT          D.1525                                                                             °C.                                                                        123  126  130  133                                    Flexural Modulus                                                              at 23° C.                                                                             D.790                                                                              MPa 1450 1440 1430 1550                                   at 80° C.                                                                             D.790                                                                              MPa 250  250  260  280                                    IZOD                                                                          at +23° C.                                                                            D.256                                                                              J/m 820 PR                                                                             925 PR                                                                             910 PR                                                                             890 PR                                 at -15° C.                                                                            D.256                                                                              J/m 190  650 PR                                                                             820  260                                    at -40° C.                                                                            D.256                                                                              J/m 100  450  250  150                                    Distortion Temperature (HDT)                                                  under 4.5 kg   D.648                                                                              ° C.                                                                       80   81   85   97                                     under 18.2 kg  D.648                                                                              °C.                                                                        45   47   47   48                                     __________________________________________________________________________     PR = Partially cracked.                                                  

EXAMPLES 5-7

By operating under the same conditions as in Examples 1-4, granules areprepared from blends consisting of:

(a) polybutyleneterephthalate having a viscosity of 1.4 dl/g;

(b) polybutylacrylate grafted with methylmethacrylate, having a gelcontent of 91% by weight, and a glass transition temperature (T_(g)) of-50° C., manufactured by Rohm and Haas under the tradename KM 323 B; and

(c) copolyesters obtained from terephthalic acid, 1,4-butanediol andpolyoxytetramethyleneglycol, with a molecular weight of about 1000, andhaving different contents of rigid segments, as reported in Table 2below.

During the preparation of these blends, 0.8% by weight of anti-oxidants,as already specified in the foregoing examples, were also added.

The weight ratios between the blend components and the properties asdetermined on the specimens obtained from said blends, are reportedbelow in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                            Example No.                                           Composition             5    6    7                                           __________________________________________________________________________    (a) Polybutyleneterephthalate                                                                         74.2 74.2 74.2                                        (b) Rubber KM 323 B     25   20   20                                          (c) Copolyester containing:                                                   33% of rigid segments        5                                                46% of rigid segments             5                                           (d) Antioxidants        0.8  0.8  0.8                                         __________________________________________________________________________                            Example No.                                           Specific       D.720                                                                              g/cm.sup.3                                                                        1.22 1.21 1.22                                        Gravity at 23° C.                                                      Yield Strength D.638                                                                              MPa 38   35   37                                          VICAT          D.1525                                                                             °C.                                                                        120  110  120                                         Flexural Modulus                                                              at 23° C.                                                                             D.790                                                                              MPa 1650 1550 1620                                        at 80° C.                                                                             D.790                                                                              MPa 360  320  340                                         IZOD                                                                          at +23° C.                                                                            D.256                                                                              J/m 600 PR                                                                             820 PR                                                                             650 PR                                      at -15° C.                                                                            D.256                                                                              J/m 200  650 PR                                                                             450 PR                                      at -40° C.                                                                            D.256                                                                              J/m 100  160  140                                         Distortion Temperature (HDT)                                                  under 4.5 kg   D.648                                                                              °C.                                                                        85   75   84                                          under 18.2 kg  D.648                                                                              °C.                                                                        48   45   46                                          __________________________________________________________________________     PR = Partially cracked.                                                  

EXAMPLES 8-11

Examples 1-4 are repeated, with polybutyleneterephthalate being replacedby a mixture of polybutyleneterephthalate/polyethyleneterephthalate in40:60 weight ratio.

The compositions of the blends, and the properties of the specimensobtained from said blends are reported in the following Table 3:

                                      TABLE 3                                     __________________________________________________________________________                            Example No.                                           Composition             8    9    10   11                                     __________________________________________________________________________    (a) 40:60 Polybutylene- 74.2 74.2 74.2 74.2                                   terephthalate/polyethylene-                                                   terephthalate blend                                                           (b) Rubber KM 653       25   20   20   20                                     (c) Copolyester containing:                                                   33% of rigid segments        5                                                46% of rigid segments             5                                           66% of rigid segments                  5                                      (d) Antioxidants        0.8  0.8  0.8  0.8                                    __________________________________________________________________________                            Example No.                                           Properties     Method                                                                             Unit                                                                              8    9    10   11                                     __________________________________________________________________________    Specific       D.720                                                                              g/cm.sup.3                                                                        1.23 1.225                                                                              1.225                                                                              1.227                                  Gravity at 23° C.                                                      Yield Strength D.638                                                                              MPa 40   38   37   39                                     VICAT          D.1525                                                                             °C.                                                                        120  125  127  130                                    Flexural Modulus                                                              at 23° C.                                                                             D.790                                                                              MPa 1550 1480 1570 1590                                   at 80° C.                                                                             D.790                                                                              MPa 300  260  290  290                                    IZOD                                                                          at +23° C.                                                                            D.256                                                                              J/m 700  900  800  850                                    at -15° C.                                                                            D.256                                                                              J/m 170  750  600  550                                    at -40° C.                                                                            D.256                                                                              J/m 80   600  450  320                                    Distortion Temperature (HDT)                                                  under 4.5 kg   D.648                                                                              °C.                                                                        80   77   79   78                                     under 18.2 kg  D.648                                                                              °C.                                                                        54   49   50   52                                     __________________________________________________________________________

EXAMPLES 12-15

By operating under the same conditions as in Examples 1-4, blends areprepared which consist of:

(a) polybutyleneterephthalate having a viscosity of 1.4 dl/g;

(b) butadiene rubber of the KM 653 type, manufactured by Rohm and Haas;

(c) copolyester obtained from terephthalic acid, 1,4-butanediol, andpolyoxytetramethyleneglycol, having a molecular weight of about 1000,and having a content of rigid segments of 33%; and

(d) polycarbonate obtained from phosgene and bisphenol A, manufacturedby ENICHEM under the tradename SINVET 271, or thermoplastic polyurethanemarketed by UPJOHN under the tradename ISOPLAST 201.

The compositions of the blends and the properties of the specimensobtained from said blends are reported in the following Table 4.

                                      TABLE 4                                     __________________________________________________________________________                            Example No.                                           Composition             12   13   14   15                                     __________________________________________________________________________    (a) Polybutyleneterephthalate                                                                         67.2 67.2 67.2 67.2                                   (b) Rubber KM 653       25   20   25   20                                     (c) Copolyester              5         5                                      (d) Polycarbonate SINVET 271                                                                          7    7                                                Polyurethane ISOPLAST 201         7    7                                      (d) Antioxidants        0.8  0.8  0.8  0.8                                    __________________________________________________________________________                            Example No.                                           Properties     Method                                                                             Unit                                                                              12   13   14   15                                     __________________________________________________________________________    Specific       D.720                                                                              g/cm.sup.3                                                                        1.198                                                                              1.208                                                                              1.200                                                                              1.203                                  Gravity at 23° C.                                                      Yield Strength D.638                                                                              MPa 42   34   42   32                                     VICAT          D.1525                                                                             °C.                                                                        120  135  125  132                                    Flexural Modulus                                                              at 23° C.                                                                             D.790                                                                              MPa 1350 1500 1420 1380                                   at 80° C.                                                                             D.790                                                                              MPa 220  250  240  230                                    IZOD                                                                          at +23° C.                                                                            D.256                                                                              J/m 980 PR                                                                             1050 PR                                                                            200  850 PR                                 at -15° C.                                                                            D.256                                                                              J/m 900  1030 PR                                                                            180  880 PR                                 at -40° C.                                                                            D.256                                                                              J/m 300   900 PR                                                                            80   350 PR                                 Distortion Temperature (HDT)                                                  under 4.5 kg   D.648                                                                              °C.                                                                        88   75   78   70                                     under 18.2 kg  D.648                                                                              °C.                                                                        49   46   52   50                                     __________________________________________________________________________     PR = Partially cracked.                                                  

Although the invention has been described in conjunction with specificembodiments, it is evident that many alternatives and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, the invention is intended to embrace all ofthe alternatives and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A polymeric composition comprising:(a) from 55 to98% by weight of a saturated polybutyleneterephthalate polyester; (b)from 1 to 35% by weight of a butadiene/styrene/methyl methacrylateterpolymer rubber containing from 58-62% by weight polybutadiene, from12-18% by weight styrene and from 24-26% by weight methylmethacrylate,and having a cross-linking degree, gel content, of 94-99% by weight witha Tg less than 0° C.; (c) from 1 to 10% by weight of an blockcopolyester having a melting point lower than 190° C., and obtained bypolycondensation or transesterification of an aromatic dicarboxylic acidwith diol having the formula (I)

    HO--R--OH                                                  (I)

wherein R is a linear or branched alkylene radical containing 2 to 20carbon atoms, or an arylene or cycloalkylene radical containing from 6to 20 carbon atoms, and with a polyetherglycol having the formula:

    HO--(R.sub.1 --O).sub.m --H                                (II)

wherein R₁ is a linear or branched alkylene radical containing from 2 to20 carbon atoms, and m is an integer greater than 2, and such that themolecular weight of the polyetherglycol is within the range of from 300to 10,000; and (d) from 1 to 25% of a thermoplastic material selectedfrom polycarbonates and polyurethanes relative to the total composition.2. The polymer composition of claim 1, wherein the molecular weight ofthe polyetherglycol is within the range of from 600 to
 4000. 3. Apolymeric composition according to claim 1, wherein theblock-copolyester has a content of rigid segments within the range offrom 10 to 75% by weight, and the ratio of the number of carbon atoms tothe number of oxygen atoms in the flexible segments is equal to orgreater than
 2. 4. A polymeric composition according to claim 1, whereinthe block-copolyester has a content of rigid segments within the rangeof from 30 to 50% by weight, and the ratio of the number of carbon atomsto the number of oxygen atoms in the flexible segments is equal to orgreater than
 2. 5. A polymeric composition according to claim 1, furthercontaining at least one additive selected from the class consisting ofstabilizers, antioxidants, pigments, dyes, flame-proofing agents,lubricants, organic and inorganic reinforcing agents, and nucleatingagents.
 6. A polymeric composition according to claim 1, wherein theterpolymer rubber is in the form of particles having a size within therange of 0.1 to 2 microns.
 7. The composition of claim 1, wherein the Tgis equal to -80° C.
 8. The composition of claim 1, wherein thecross-linking degree gel content is 94% by weight.
 9. The compositionaccording to claim 1, wherein the intrinsic viscosity of thepoly(butylene terephthalate) is 1.4 dl/g.